Abstract:

The invention relates to a chassis component for an automobile and a
method for producing such chassis component. A mineral core body made of
silicate is cast inside a light metal casting, and the blank produced in
this manner is processed by forging, forming they chassis component 1.
The density and strength of the base body of the light metal casting
forming the chassis component as well as of the core body can be adjusted
during the forging process.

Claims:

1.-16. (canceled)

17. A chassis component for an automobile, comprising:a base body made of
a light metal casting, andat least one mineral core body embedded in the
base body,wherein the base body is cast around the at least one mineral
core and the chassis component is formed by forging.

26. The chassis component of claim 17, wherein the core body is arranged
in a region of the chassis component, which has less strength, but
identical or higher stiffness, than another region of the chassis
component.

27. A method for producing a chassis component, comprising the steps
of:providing a mineral core body;casting the core body in a light metal
casting to produce a blank; andprocessing the blank by forging to form
the chassis component.

28. The method of claim 27, further comprising the steps of:grinding
rock-like vermiculite; andproducing the mineral core body from the ground
vermiculite.

29. The method of claim 28, further comprising the step of releasing
crystalline-bound water residing in the ground vermiculite in a thermal
expansion process.

30. The method of claim 29, further comprising the step of pressing the
vermiculite into a desired shape commensurate with the core body in a
temperature-dependent pressure process with addition of a
high-temperature-resistant mineral binder.

31. The method of claim 30, further comprising the step of preparing a
surface of the shaped core body with a heat-resistant mineral material.

32. The method of claim 27, wherein the core body is made from silicate.

33. The method of claim 27, wherein the core body is made from
aluminum-iron-magnesium-silicate.

36. The method of claim 27, wherein a density or a strength, or both, of
the core body are adjusted during forging.

37. The method of claim 27, wherein the blank is forged at a temperature
between 400.degree. C. and 600.degree. C.

Description:

[0001]The invention relates to a chassis component for an automobile and
to a method for its manufacture.

[0002]Light metal and light alloys, in particular aluminum, become
increasingly important in the automobile industry as a lightweight
construction material, in particular for lightweight chassis components.
Because of the elasticity module is smaller than that of steel, the
required stiffness of the components requires special cladding-like
structures take advantage of the lightweight construction potential of
the light metal materials. For highly stressed chassis components, such
as hinge bearings, triangular control arms and transverse control arms,
which require yield strengths of about 350 MPa at a simultaneously high
ductile yield of at least 10%, light metal hollow cast chassis parts can
no longer be used or only in limited ways, because these attain yield
strengths of only about 200 MPa and ductile yields of about 5%.

[0003]It is presently routine to produce such highly stressed chassis
components by drop-forging from preformed forging blanks based on
extruded profiles. In this context, the so-called Cobapress method is
also state-of-the-art. This is a hybrid method where a cast blank is
reforged once. The cast structure is hereby compacted by the impact force
during drop forging. Porosities typical with castings, shrinkage cavities
and other structural defects are comminuted and welded when the material
flows during welding, so that the yield strength can be increased to
about 280 MPa and the ductile yield to about 10%.

[0004]The so-called counterpressure casting is also used in the
manufacture of chassis components. In the counterpressure method, an
overpressure is produced during the solidification phase of the light
metal cast in the mold. This also significantly reduces casting-related
porosities, shrinkage cavities and other structural defects and increases
the yield strength to about 260 MPa and the ductile yield to about 10%.

[0005]The conventional methods have proven successful in operation.
However, with the conventional methods, the required component
characteristic properties of chassis components can only be realized as
solid parts with full cross-sections. The requirements for higher
strengths which are limited to certain regions therefore determine the
entire component, although the components have other regions where the
requirements with respect to strength are reduced, but where a higher
stiffness is required. This higher stiffness in certain regions can be
with conventional approaches only be achieved by increasing the full
cross-sections, which leads to a fundamentally unnecessary increase in
weight and material consumption.

[0006]It is therefore an object of the invention to obviate the
shortcomings of the state-of-the-art and to reduce the weight of highly
stressed chassis components with yield strengths between about 280 MPa
and 300 MPa and with ductile yields of about 10% or more, while
maintaining in all other aspects the requirements for local strength and
stiffness, to reduce material consumption and to thereby form the
components more economically, and to provide a method for producing a
highly stressed lightweight chassis component.

[0007]The part of the object relating to the device is attained with a
chassis component according to claim 1.

[0008]The chassis component according to the invention has a base body of
a light metal casting. A mineral core body is embedded by casting in the
base body. The base body together with the embedded mineral core body is
processed by forging and formed into the chassis component.

[0009]Because the stiffness is determined by the third power of the
distance to the neutral centerline of the chassis component, the outer
cross-sectional regions of the chassis components are particularly
important, whereas the inner regions contribute little to the stiffness.
This realization forms the basis for the invention. Advantageously, the
weight can be reduced while maintaining the same stiffness by designing
the components not with full cross-sections, but by at least partially
using a light core material in the interior and applying an outer layer
which determines the stiffness.

[0010]The base body forming the outer cladding of the chassis component is
made of a light metal casting. Particularly suitable materials are
aluminum and aluminum alloys, or magnesium or magnesium alloys.

[0011]A mineral material which is more heat-resistant and lighter than the
material of the outer base body made from a light metal casting may be
used as the core body. The heat and temperature resistance is such that
the core body can be embedded in the molten hot light metal casting.
Aluminum or aluminum alloys have a specific weight of about 2.7
g/cm3 and a melting point of about 660° C. Magnesium or
magnesium alloys have a specific weight of about 1.7 g/cm3 and a
melting point of about 650° C. Preferably, the material to be used
as the core body should have a refractory quality to withstand
temperatures of 800° C. and higher, in particular a melting point
between 1300° C. and 1400° C. In this context, in
particular materials based on expanding clay minerals are contemplated.
One example of such material is vermiculite.

[0012]The core body is particularly arranged in those regions of the
chassis component which should have less strength, but the same or a
higher stiffness, than other regions of the chassis component.

[0013]Preferably, the core body is made of a silicate, in particular of
aluminum-iron-magnesium-silicate.

[0014]The part of the object relating to the method is attained with a
method according to claim 8.

[0015]According to the invention, the employed forging blanks are cast
parts which are formed in accordance with the component and which have a
core body made from lightweight, heat-resistant and thermally stable
materials. The core bodies must be able to withstand the subsequent drop
forging processes, heat treatments, mechanical machining as well as
stress in the chassis component and remain as a permanent core in the
chassis component.

[0016]According to the invention, the core body is produced by initially
providing a rock-like vermiculite starting material. The starting
material is ground to a predetermined particle size. The ground
vermiculite particles are then processed in a special thermal expansion
process, thereby releasing crystalline-bound water. The volume of the
vermiculite particles increases when the crystalline-bound water is
released. The vermiculite particles treated in this way are then pressed
in an additional temperature-pressure controlled processing process with
addition of a high-temperature-resistant mineral binder into the desired
shape of the core body. A core body produced according to the invention
is, depending on the desired shape to be produced, about three times to
five times lighter than a conventional component made, for example, from
aluminum foam.

[0017]To prevent porosities caused by outgassing of the air inclusions
contained in the hybrid cores, as well as to protect against damage from
transport and handling, surface of the core body may optionally be
specially prepared with heat-resistant mineral materials.

[0018]The core bodies are arranged in a stable position in a casting mold
and subsequently cast and encapsulated in a light metal casting. The
position of the core body or bodies is adapted to the later stresses of
the finished vehicle component. The core bodies are arranged at those
locations where primarily a higher stiffness, rather than a higher
strength is required. The core bodies are already positioned in the blank
in conformance with the characteristics and the contour of the
components. The forging process, for example drop forging, is then
performed so that the light metal material and the core body are
compacted in a defined manner during forging, whereby the required
mechanical properties of the chassis component can be attained or
adjusted. The temperatures are defined by the forging process. In
practice, the forging temperatures can be assumed to be between
400° C. and 600° C. The blank can be processed by forging
after the blank is cast to take advantage of the heat generated in the
casting process. In principle, a cold blank for the forging process can
also be heated to the forging temperature.

[0019]Those regions of the chassis component requiring the highest
strength are produced as before with a full cross-section. The material
attains the highest strength in these component regions through a
corresponding material flow and material compaction during the forging
process.

[0020]Depending on the requirements, different properties can be
intentionally introduced into the chassis components, depending on the
positions and the design of the core bodies, on the regions of the
chassis components with full cross-section as well as the of the setting
of the degree of deformation and the flow characteristic of the forging
blank during forging. Depending on the setting for the mechanical
properties and the density of the core body before and after forging, an
additional inner supporting effect and increase in the stiffness can also
be attained in the region of the core body in the chassis component.

[0021]The forging process according to the invention is designed to
require only a low forming pressure for producing the forged hybrid
component in the region of the core body embedded in the forging blank.
This results in a very small material flow and likewise a very small
material reforming in the forged hybrid component. The hybrid component
has therefore locally differentiated required mechanical properties in
its finished form, without also upsetting the core body in the forging
process so as to increase its density. As a result, a particularly
lightweight forged hybrid component with an embedded vermiculite body is
produced with the method of the invention.

[0022]The invention provides chassis components capable of withstanding
high stress with yield strengths to about 280 MPa and ductile yields to
about 10%, which also have a lower weight than comparable conventional
chassis components. With identical stiffness, the method of the invention
is capable of reducing the weight of the chassis components compared to
the state-of-the-art. This is not only an important factor for reducing
the manufacturing costs, but also an important contribution for reducing
the mass of the chassis components, in particular unsprung masses which
greatly affect the energy consumption and the driving comfort.

[0023]The invention will be described hereinafter with reference to the
appended FIGURE.

[0024]The FIGURE shows a chassis component according to the invention in
form of a forged hinge bearing 1. The hinge bearing 1 includes a base 2
made of a light metal casting. In particular, the base body 2 can be made
from aluminum, an aluminum alloy, but also from magnesium or a magnesium
alloy. A mineral core body 3 is embedded in the base body 2 by casting.

[0025]The core body 3 is made from a silicate, in particular from an
aluminum-iron-magnesium-silicate.

[0026]The FIGURE illustrates that the core body 3 is arranged in a center
region 6 of the component which extends between the lower region 4 of the
component and an upper region 5 of the component. This longitudinal
extent of this region 6 of the component is indicated with the reference
symbol A. The core body 3 is schematically illustrated in the FIGURE in
combination with an illustration of a cross-section through the region 6
of the component. The region A of the component has particularly high
stiffness requirements. In this region, the core body 3 can reduce the
weight while maintaining a high stiffness. The regions of the component
indicated in the FIGURE with the reference symbol B are subject to
primary strength requirements. For this reason, the regions B of the
component are produced in a conventional manner with a full
cross-section.

[0027]For producing the hinge bearing 1, a prefabricated mineral core body
3 is provided with a geometry adapted to the subsequent use in the
chassis component. This core body 3 is positioned in a casting mold and
cast in a molten light metal casting and thus embedded in the light metal
casting. The blank produced in this manner is then machined by forging,
thereby forming the hinge bearing 1. During the forging process, the
density and/or the strength of the hinge bearing 1 are intentionally
adjusted. The blank can be processed by forging after the blank is cast,
using thermal energy from the casting process. However, a cooled blank
can also be heated for the forging process to the forging temperature.

LIST OF REFERENCE SYMBOLS

[0028]1 Hinge bearing [0029]2 Base body [0030]3 Core body [0031]4 Lower
region of the component of 1 [0032]5 Upper region of the component of 1
[0033]6 Center region of the component of 1 [0034]A Region of the
component [0035]B Region of the component